Westchester County District Attorney Jeanine Pirro received two major boosts in her campaign against Sen. Hillary Clinton yesterday when she picked up Gov. Pataki’s endorsement and her chief Republican rival abruptly quit.

But Pirro also suffered a major setback as Clinton filed a campaign finance report showing she raised nearly $5.3 million during the last three months – more than 10 times the $438,555 collected by Pirro over the same period.

Gleeful Clinton backers said Pirro’s fund-raising showed how weak her political support was. They also noted that in the 2000 Senate race, opponents Rudy Giuliani and then Rick Lazio raised more than $5 million each in their respective first quarters against the former first lady.

Pataki’s support for Pirro, who has been running nearly 30 points behind Clinton in recent polls, had been expected, but the decision by Manhattan lawyer Edward Cox, former President Richard Nixon’s son-in-law, to exit the race was not.

Cox, who had cast himself as far more conservative than Pirro and spent months traveling the state to make his case to local GOP officials, was widely seen as gaining support at Pirro’s expense among GOP and Conservative Party leaders, especially upstate.

But Cox released a late-afternoon statement citing Pataki’s endorsement of Pirro and saying it was time to end his campaign.

“Out of respect for [Pataki’s] position and his decision, I have decided to stop my campaign for the U.S. Senate,” said Cox, who had repeatedly promised to remain in the race at least until the state GOP convention next spring.

Some have suggested Cox could now run for attorney general or Congress, but his campaign had no comment on his plans.

Cox’s decision stunned Conservative Party Chairman Mike Long, who had praised his campaign and expressed strong reservations about Pirro’s moderate to liberal positions on abortion and gay rights.

“In all honesty, I’m surprised,” Long said. “He was running an effective campaign, reaching out to both Republican and Conservative Party leaders.”

Cox’s decision leaves former Yonkers Mayor John Spencer, who also enjoys considerable Conservative backing, and little-known Sullivan County resident William Brenner as the only Republicans left to challenge Pirro.

Clinton, who is currently on a California fund-raising swing, reported raising nearly $5.3 million in the three-month period ending Sept. 30, bringing her total cash on hand to more than $13.8 million.

By contrast, Pirro had $363,920 in the bank.

Pataki, meanwhile, appeared with Pirro yesterday at the Women’s National Republican Club in Manhattan and said New Yorkers know “we can count on her toughness and determination to get things done for us in Washington.”

“I know Jeanine Pirro to be a tough, hard-charging, district attorney and former judge who has made protecting our children and families her top priority,” Pataki said.